Phase-coded control for ring laser gyro

Abstract

In a laser gyro, laser optics adjustment means comprising a mirror within the laser optics of the gyro and mounted upon a three-terminal duo-mode bimorph device for duo-mode modulation of the laser optics. A two-stage differential amplifier is responsively coupled to a source of two mutually phase-coded reference signals for separately dithering each mode of the duo-mode bimorph device, each stage being further responsive to a mutually exclusive one of a first and second synchronously detected photodetector output of the laser gyro whereby closed loop control of the laser optics is effected.

I claim: 
     
       1. A dual phase-coded control means for control of a three-terminal duo-mode bimorph device having a translational control mode terminal and torsional control mode terminal pair and comprising a source of two mutually phase-coded and selectively biased a-c reference signals, and   a dual mode differential amplifier interconnecting said source to said terminal of said bimorph device for dithering each mode of said dual mode bimorph device in response to a mutually exclusive one of said reference signals, said amplifier further having a first and second control input adapted to be coupled to a respective one of two sources of a bipolar control signal for control of a mutually exclusive mode of said duo-mode bimorph device.   
     
     
       2. The device of claim 1 in which said differential amplifier is comprised of two differential amplifier stages, each stage having a first control input terminal and a second dither input terminal, and a differential output terminal pair;   a second input terminal of each of said two amplifier stages responsive to a mutually exclusive one of said two reference signals of said source,   a pair of differential output terminals of said second amplifier connected to said torsional control mode terminal pair of said bimorph device, a centertapped impedance being connected across said terminal pair connection and comprising a terminal of a supply voltage source for said differential amplifier,   a first terminal of a differential output terminal pair of said first stage being connected to a common terminal of said second stage and a second output terminal of said first stage being connected to said translational control mode terminal of said bimorph device;   a coupling impedance connected across said translational mode control terminal and a center tap terminal of said centertapped impedance; and   a high impedance current source interconnecting a common terminal of said first stage and a ground terminal of a supply voltage source for said differential amplifier.   
     
     
       3. The device of claim 2 in which each said differential amplifier comprises a pair of like-poled transistors, each transistor having a base electrode, a collector and an emitter, the emitters of each pair being connected together to form a common terminal, said collectors of each said pair comprising differential output signalling terminals, said bases of each such pair comprising a respective first control and second dither input terminal. 
     
     
       4. In a laser gyro, laser optics adjustment means comprising a mirror within the laser optics of said laser gyro mounted upon a three-terminal duo-mode bimorph device for duo-mode modulation of said optics, and   a two-stage differential amplifier responsively coupled to a source of two mutually phase coded reference signals for separately dithering each mode of the duo-mode bimorph device, each stage being further responsive to a mutually exclusive one of a first and second synchronously detected photodetector laser output of said laser gyro, whereby closed loop control of said laser optics is effected.   
     
     
       5. The device of claim 4 in which said two-stage differential amplifier comprises a first stage having a common terminal coupled to a first terminal of a power supply by a high impedance current source, a first input terminal adapted to be responsive to a first one of said synchronously detected photodetected laser outputs, and a second input terminal of said first stage being responsive to a first one of said phase-coded reference signals, one of two output terminals of said first stage being connected to a said first mode single terminal of said bimorph device,   a said second stage having a common terminal coupled to another output terminal of said two output terminals of said first stage, a first input terminal of said second stage being adapted to be responsive to a second one of said synchronously detected photodected laser outputs and a second input terminal of said second stage being responsive to a second one of said phase-coded reference signals, each of two output terminals of said second stage being connected to a mutually exclusive one of two terminals of a second mode terminal pair of said bimorph device,   a second terminal of said power supply being impedance coupled to each of said three terminals of said bimorph device by a mutually exclusive one of three separate impedances, the two impedances coupling said second mode terminal pair of said bimorph device being substantially equal.   
     
     
       6. The device of claim 5 in which each stage of said two-stage differential amplifier comprises a pair of like-poled transistors, each transistor having a base electrode, a first electrode and a second electrode, the first electrodes of each transistor pair being connected to form a common terminal, the second electrode of each transistor of said transistor pair comprising a respective first and second output terminal, the base electrode of each transistor of said transistor pair comprising a respective first and second input terminal. 
     
     
       7. The device of claim 4 in which there is further provided a first and second phase detector, each commonly responsive to a photodetected output of said laser,   a reference input of said first detector being responsive to one of said phase coded reference signals for providing a phase detected control signal output to said differential amplifier for control of that bimorph control mode which is dithered by said one of said phase coded reference signals, and   a reference input of said second phase detector being responsive to the other of said phase coded reference signals for providing a phase detected control signal output to said differential amplifier for control of that bimorph control of that bimorph control mode which is dithered by said other of said phase coded reference signals.   
     
     
       8. In a laser gyro having laser optics adjustment means comprising a mirror within the laser optics of said laser gyro mounted upon a three-terminal duo-mode bimorph device for duo-mode modulation of said optics   a two-stage differential amplifier responsively coupled to a source of two mutually phase coded reference signals for separately dithering each mode of the duo-mode bimorph device,   and a first and second detector commonly responsive to the photodetected laser output of the laser gyro, each phase detector having a reference input responsive to a mutually exclusive one of said phase coded reference signals for providing a synchronously detected output, said differential amplifier being further responsive to each of said first and second synchronously detected outputs of closed loop control of said laser optics is effected.   
     
     
       9. The device of claim 8 in which said two-stage differential amplifier comprises a first stage having a common terminal coupled to a first terminal of a power supply by a high impedance current source, a first input terminal adapted to be responsive to a first one of said synchronously detected outputs, and a second input terminal of said first stage being responsive to a first one of said phase-coded reference signals, one of two output terminals of said first stage being connected to said first mode single terminal of said bimorph device,   a said second stage having a common terminal coupled to another output terminal of said two output terminals of said first stage, a first input terminal of said second stage being adapted to be responsive to a second one of said synchronously detected outputs and a second input terminal of said second stage being responsive to a second one of said phase-coded reference signals, each of two output terminals of said second stage being connected to a mutually exclusive one of two terminals of a second mode terminal pair of said bimorph device,   a second terminal of said power supply being impedance coupled to each of said three terminals of said bimorph device by a mutually exclusive one of three separate impedances, the two impedances coupling said second mode terminal pair of said bimorph device being substantially equal.   
     
     
       10. The device of claim 8 in which the two stage differential amplifier comprises a first pair of like-poled transistors, each transistor having   a first, second and base electrode, the first electrodes of said first pair being common terminal coupled to a first terminal of a power supply,   the base terminal of a first transistor forming a first input terminal adapted to be responsive to a first one of said synchronously detected outputs,   the base terminal of a second transistor forming a second input terminal responsive to a first one of said phase-coded signls,   the second electrode of said second electrode being connected to said first mode single terminal of said bimorph device;     a second pair of like-poled transistors, each transistor having a first, second and base electrode, the base terminal a first transistor of said second pair being adapted to be responsive to a second one of said synchronously detected outputs,   the first electrodes of said second pair being commonly connected to form a second common terminal,   the base terminal of a second transistor of said second pair being responsive to a second one of said phase coded reference signals,   each of the second electrodes of said second pair being connected to a mutually exclusive one of two terminals of a second terminal pair of said bimorph device;     a second terminal of said power supply being impedance coupled to each of said three terminals of said bimorph device by a mutually exclusive one of three separate impedances, the two impedances coupling said second mode terminal pair of said bimorph device being substantially equal.